During radiology procedures, and in particular, during angiography, it is often necessary to determine the size of structures or chambers within the body. Because there is an unknown magnification factor relating the actual size of structures to be measured with the images formed on film, it is desirable to have an object of known dimensions with which to compare the body structure.
Catheters, grids of known dimensions and radiopaque cubes of known dimensions are all commonly used as radiography scaling devices, but all have certain inherent disadvantages. If a catheter of known diameter is in the picture, this may be used. However, the catheter must be at the same location as the structure to be imaged, preferably through the structure to be imaged, or an unknown magnification error will result. For more precise measurement, a picture of a grid or a radiopaque cube of known dimensions may be imaged. For the image to be useful, the grid should be the same distance from the imaging beam as the body structure to be measured, and the grid must be positioned so that its known dimension is perpendicular to the imaging beam.
Frequently, it is necessary to image a body structure with views other than straight AP and lateral and often these views are non-orthogonal. If a cube or a grid is used as the reference for a non-orthogonal image, much time is spent tediously positioning the cube or grid so that it is perpendicular to the first image axis, then repositioning it to be perpendicular to the second axis; it is impossible to film the cube or grid with two non-orthogonal cameras simultaneously, as the beams cannot both be perpendicular to the reference object. Furthermore, to obtain a precise reference, it is important for the reference object to be positioned in the same relative position in three dimensional space, with reference to two imaging beams, as the body structure was when the image of the structure was taken. This requires positioning the reference object accurately in order for it to appear in the same place as the body structure on both images simultaneously.
When catheters are used, the catheter diameter is the known image dimension. If a catheter diameter is used as the reference dimension, there may be an inherent inaccuracy unless the catheter is adjacent to or through the body structure being measured, so that it is accurately positioned at the location of interest. Also, because the images of the edges of plastic catheters tend to fade and the catheter casts an image with a small diameter, it may be difficult to precisely measure the catheter diameter. Accordingly, a catheter diameter is an inherently poor reference object.
For all of these reasons, there remains a need for an improved radiography scaling device and method; particularly one which lends itself to image scaling in multiple views.